We report the design, fabrication, and experimental demonstration of active narrowband multiple wavelength filters in
aperiodically poled lithium niobate (APLN) crystals. We obtained the simultaneous transmission of 8 ITU standard
wavelengths with transmittance of >90% (~100% in design) and a bandwidth of ~0.45 nm from a 5-cm long APLN Solctype
filter. Four peak-narrowed and highly sidelobe-suppressed second-harmonic generation (SHG) signals of four
telecom wavelengths from a monolithic LiNbO<sub>3</sub> crystal cascading a 1-cm long APLN wavelength filter and a 1-cm long
APLN wavelength converter was also obtained.